The present invention relates to fluid pressure valves and, in particular, vacuum valves for providing a vacuum control signal for control of automotive engine accessories and emission control devices. In the operation of such devices it is often necessary to change the vacuum control signal by alternately providing communication of the control signal port with separate vacuum sources in response to predetermined levels of engine temperature. For example, from a cold start, it is necessary to provide a given high-magnitude vacuum signal to the signal port of the valve until the engine reaches a certain temperature level, at which time it is required to provide a different level vacuum signal to the control signal port. This is ordinarily accomplished by providing a vacuum valve operated by a thermal sensing unit which senses the engine temperature. For convenience, the thermal sensing unit and the valve are combined as an integral unit, and the assembly is threaded into a hole in a suitable part of the engine such as the cylinder head water jacket or the intake manifold with the thermal sensing element exposed to the temperature of the appropriate portion of the engine structure.
In the above type of device it is often desired to provide fluid communication between a vacuum signal port and a first source of vacuum and, by valving action, isolate the vacuum signal port from the first vacuum source and provide communication of the signal port with a second vacuum source. The signal port is, in such known devices, fluidically a common port between two valve seats which are opened and closed substantially simultaneously. Previous devices providing such a vacuum valving function have employed an operating pushrod extending from a thermal sensing unit to progressively unseat and seat a check ball from separate valve seats for providing the valving between the common signal port and the separate vacuum source ports. Where such check ball structures have been used, it has been required to provide a precisely controlled degree of thermal sensitivity to accomplish the valving function in the desired temperature change in order that the pushrod not exert excessive force on the check ball during over-travel. Previous attempts to provide for over-travel of the pushrod through a broader temperature range have utilized a movable valve seat for the check ball. However, in providing such a movable valve seat, it has been found difficult to provide a suitable moving seal with the valve body.
Where it is desired to provide a combined fluid pressure valve function with actuation of an electrical switching means simultaneously at a given temperature level, it has been necessary to provide a separate actuator member responsive to movement of the check ball for actuation of the electrical switch means. In this latter type of arrangement, the thermal sensitivity of the pushrod is limited by check ball travel which has caused difficulty in providing proper actuation of the electrical switching means.